The present invention relates to bonding pad structures and methods of making same, and pertains particularly to a raised bonding pad structure for III-V compounds.
Many semiconductor devices are connected into electronic circuits by means of conductors connected by bonding pads or the like. Bonding pads and leads must be carefully constructed and selected to match the characteristics of the elements being placed in the circuit. The connection of metallic leads to class III-V compounds ia a particular problem because of the capability of such compound elements to function at elevated temperatures. The customary bonding pads suitable for silicon devices has been found not to be suitable for the group III-V compounds.
Many of the problems of formation of bonding pads to group III-V compound semiconductors are set out in an article or paper entitled "A Review of the Theory and Technology for Ohmic Contacts to Group III-V Compound Semiconductors" by V. L. Rideout, published in the Solid State Electronics 1975, Volume 18 at pages 541 through 550, by Pergamon Press, printed in Great Britain. This publication sets out the background and an introduction to group III-V compound semiconductors and also points up some of the problems of the formation of Ohmic contacts for such compound semiconductors. Various prior art approaches to this problem for such compounds are also set out in this paper. These, however, have not proven entirely satisfactory for certain applications. The applicants of the present invention have devised the present invention to overcome numerous problems which have not been solved by the prior art.
The prior art approach to the formation of bonds to bonding pads to certain group III-V semiconductor compound bodies is also illustrated in the following U.S. Patents.
U.S. Pat. No. 3,214,654, issued Oct. 26, 1965 to Armstrong et al, directed to ohmic contacts to III-V semiconductive compound bodies. This patent sets forth several examples of the fabrication of ohmic contacts to semiconductor III-V compound bodies. However, he does not suggest the use of nickel chromium as the first layer of contact layer. He also does not recognize the advantage of using palladium as a metalization layer.
U.S. Pat. No. 3,406,050, issued Oct. 15, 1968 to Shortes, is directed to a method of making electrical contact to a semiconductor body. This patent discloses an approach to the formation of bonding pads for semiconductor materials, such as gallium arsenide. This patent discloses the use of high melting point refractory metals having a higher melting point than that of the wafer for attachment to the wafer. However, he does not disclose the applicant's approach to the formation of ohmic contacts.
U.S. Pat. No. 3,831,068, issued Aug. 20, 1974 to Kniepknap is directed to metal semiconductor small surface contacts. In this patent, contact for gallium arsenide semiconductor device is formed by a first layer of contact material consisting of chrome with subsequent layers of nickel, gold and silver. He does not suggest the applicant's construction.
The present invention is devised specifically for the problems of group III-V compounds and particularly for LED wafers.